Conclusion

Ever since the first bacteria appeared on earth, living beings have been evolving constantly to adapt to our everchanging world. These adaptions have lead to the animals that we see today, from the simplest sponge to the most complex chordate, such as ourselves. These adaptions occur over millions of years, and without evolution, we would not see the species diversity that we do today.

As bacteria grew more and more advanced, they began to group together to form larger, more organized masses. Something clicked that made them realize that working together could make them survive longer, and be more successful. As these basic cells grouped together, they formed the first animals. While not technically considered multicellular, they were the phylum Porifera; the sponges. Not made up of any tissue, these colonial-celled beings are the most basic animal on the planet. They have no organs, no true body cavity, and the most basic circulatory, respiratory, and digestive systems of all animals. These animals are sesile, making any hunting impossible. They reproduce randomly by releasing sperm out into the ocean, or by budding and allowing their offspring to float off to other areas of the sea floor. All their body functions rely on water; they need it to bring in food and excrete wastes as they are filter feeders. They need water to bring in oxygen for their respiratory system. And they need water to reproduce, as their sperm is spread to other sponges on ocean currents. Sponges also have no nervous system or brain, so they are unable of thought or feeling. All of these things make the sponge the least complex and advance of the kingdom animalia; however, the millions of years of existance they have had means they are still highly adapted to the life they live.

The sponges were one of the few living things on earth and in the oceans for millions of years. Eventually, a new animal came along, much more complex than the sponges. These new beings were predators, capable of movement, meaning they could hunt for their food. Even now, they are beginning to completely take over the worlds oceans, their population rising rapidly, forming colonies of billions all across the globe. Belonging to the phylum Cnidaria, the next animals along the evolutionary line are the jellyfish. As seen in plants, the jellyfish have an alternation of generations reproductive pattern, with the two phases being the polyp stage and the medusa stage. While the polyps are still fixed to the seabed, the medusa jellies are the first motile living creatures to appear on earth. This capability of movement allows the jellyfish to do many things that sponges cannot. They can flee an area if environmental conditions grow too detrimental; this also means they can move to more flourishing regions of the oceans. Movement allows jellyfish to hunt for food, instead of waiting for bits of food to float past. They can also gather together in large groups to mate, which means they can produce many more offspring than if they randomly released their gametes from all over the place. In both the polyps and medusas we can see the formation of self defence mechanisms in the form of tentacles. On these tentacles are thousands of cnidocytes, each containing a nematocyst, which it fires at its enemies in self defence as well as at its prey to subdue it before consumption. The ability to defend themselves has also aided in the flourishing of this phylum. Advances can be seen in the digestive system, with the formation of a combination mouth and anus, through which food enters the gastrovascular cavity. Nutrients from the food are absorbed in the cavity, and wastes are expelled back out though the mouth. Since the Cnidarians are also mulitcellular, we see the first formation of body tissues; however, they are only triploblastic, made up of an ectoderm (skin) and an endoderm (internal organs). There are no muscles in the jellyfish, as the mesoderm has not been formed in these animals. The first developments of a nervous system can also be seen in this phylum. While a jellyfish has no brain, it has a very primative nervous system, connecting to the first basic sensory organs, designed to pick up shadows. This aids in hunting as well as defence and navigating the more constricted areas of the ocean. While many of their systems are still just as basic as those seen in the sponges, the Cnidarians are made more advanced by their digestive system, self defence mechanisms, and the ability of movement.

As the earth continued to change, land became more suitable for life, and animals and plant began to evolve to survive there. One of the first land animals belonged to the phylum Platyhelminthes; the flatworms. These worms were the first triploblastic animals, meaning that their mesoderm could now form muscles allowing for more coordinated movement on both land and water. The free-living flatworms have a more advanced nervous than the previous animals, which also allowed for more coordinated movement. This system also showed the development of visible and more advanced sensory organs, such as the eye spots, used to detect light and dark, as well as the auricles on either side of the head, which act as ears, picking up vibrations. The flatworms can live almost anywhere in the planet, and being the first ones to migrate onto land, they had little to no competition for food and other resources. In these animals, the mouth stopped serving its secondary purpose as anus. Instead, flame cells were developed along the sides of the worm's body to expel wastes, so the mouth could be left for just consuming food. The mouth on free-living worms was moved onto the pharynx, which could extend from the body to reach food. Despite these advances, the platyhelminthes still had a simple digestive system consisting of only a gastrovascular cavity. The flatworms were hemaphroditic, meaning they posessed both female and male sex organs; however, they still avoided mating with themselves, instead mating with other worms, to increase genetic variations of the species. The circulatory and respiratory systems are about as basic as those of the sponges and jellyfish, with no heart or lungs, and oxygen being absorbed via diffusion through the skin. Parasitic flatworms began to form once the more advanced animals began to form, as these worms could survive very easily inside their host with little to no effort on their part. They didn't even have to get their own food; most lived in the small intestine of the animal, absorbing nutrients through their skin that would normally go into the hosts body. Platyhelminthes still had no true body cavity, and their muscles only aided in movement, not digestion. So, while the flatworms were still very primative beings, their ability to now live on land, more developed sensory organs, and their parasitic attributes made them more evolved than the Cnidarians.

After the flat worms, more worms began to evolve. They belonged to the phylum Nematoda; the roundworms. These worms were circular, and were the first animal to develop a body cavity. While this body cavity was technically a pseudocoelum, it still allowed for a more developed digestive system. The mesoderm was now not only beside the ectoderm, but beside the endoderm as well. This new muscle layer greatly sped up the digestion of the worms. The digestive system, instead of consisting of just a gastrovascular cavity, was made up of a mouth on the anterior of the body, an esophagus which lead to an intestine along the length of the body where nutients could be absorbed, and an anus for expelling wastes at the posterior end of the body. This improved digestive system meant that the worms could absorb more food and nutrients, and could grow bigger and move more due to an increase in energy levels. The body of both free-living and parasitic worms were made up mostly of intestines and reproductive organs. They also had a slightly more complex nervous system, with sensory organs in the free-living worms, but the system was still primative, with no true brain. The free-living members of the phylum play a very key role in composting organic materials and making fertile soil on the planet. Once more advance animals began to form, parasitic forms of the roundworms began to evolve. They, like the flatworms, lost their sensory organs, being as basic as possible and still being able to survive. These worms still have many of the basic systems in the past 3 phylums; they still posess an open circulatory system, no legs or skeleton, and still breathed through their skin. So, the increase in size and energy levels via the advancements in the digestive system and the formation of the pseudocoelum are the advances of the nematodes over the platyhelminthes.

In the next animals to form on earth, we see major development in all of the systems in the body. This next phylum are the Annelids; the segmented worms. In this phylum, we see the first examples of a basic segmented body plan, as well as a true coelum. While there are no specialized appendages, the body of the worms are divided into many segments. The earthworm has a more complex version of the digestive system found in the roundworms. Food enters in dirt through the worms mouth, and travels through its pharynx and esophagus to the crop and gizzard, where it is ground up. The food then travels through the intestine, where nutrients are absorbed into the bloodstream, and wastes are sent out of the body. The first improvements are seen here, in the exretory system. Along with having an anus for solid wastes, the worm has two tiny nephridia per body segment. The nephridia are used as kidneys; they take metabolic wastes, filter out the water to be reused in the body, and sends the wastes (ammonia) out of the body through tiny pores along the skin. The worm also has the first closed circulatory system. It consists of five hearts called aortic arches, and a complex network of veins, arteries, and capillaries. This system makes the spread of oxygen and nutrients throughout the body much more efficient. Most of the species still live on land, and the fact that they still breathed through their skin was a major disadvantage. This trait meant that the woms had to keep their skin constantly wet, which is somewhat challenging when out of the water. In the worms, they used setae, small grippers that attatched to the ground and allowed them to move more quickly than previous worms. In water-based species, the first formation of crude appendages can be seen in the form of paddles along the sides of the worm. These are used to propel the worm through the water, and makes them somewhat resemble centipedes and millipedes. These species also have more developed appendages around their mouth in the form of small pinchers used for hunting. They also display the development of very crude gills, which allow them to filter oxygen out of water and into their body instead of bringing it in through their skin. So, the further adaptation to succesful life on land using setae to move faster, the development of crude appendages for movement and hunting, and the development of more efficient digestive and circulatory systems make the Nematodes more advanced than the roundworms.

The next development in the evolution of animals moves many species back into the oceans with the formation of the phylum Mollusca; the molluscs, or shelled animals. This is a very diverse phylum, containing animals as simple as a clam to as biologically advanced as the squid and octopus. While only simple body segmentation is seen in the segmented worms, we first see the formation of specialized body regions in this phylum. The body is made up of a musclular food located on the ventral surface of the animal, which it uses for movement. Above the foot is the visceral mass, which contains the bulk of the organs. Surrounding the visceral mass is a thin layer called the mantle. This layer contains calcium carbonate, which, in some species, forms the shell. The digestive system is nearly identicle to that of the annelids, with food entering through the mouth, compsrised of two beaks and a mouth, and then traveling through the pharynx, esophagus, stomach, intestine, and back out the anus, which is unfortunately located above the head of the animal, if there is a head apparent. In this phylum, the circulatory system returns to an open plan, but they still posess a heart. Breathing though the skin does no longer occur with these animals; instead, they use gills on their bodies to filter oxygen out of water, which is sent directly to the heart. This new system of respiration is much more efficient than previous respiratory sytems in animals, as the heart is very close to the gills, so oxygen has to travel a very short distance. Animals in the class cephalopoda have formed tentacles similar to those in jellyfish, except with suction cups. These tentacles aid in the capturing of prey, as well as movement. The muscle development with the mesoderm allows in very fast movement through the water compared to their predecesors. This phylum can also be found in land, in the form of snails and slugs. They use their muscular food to move along land. They are at a disadvantage, however, as they breathe through their skin, they must constantly be moist. The paths of evolution can even be followed through the phylum, starting with the class bivalvia. The bivalves are very simple filter feeders. They have two shells that close to cover their internal organs, and attatch to rocks with their foot. They cannot, however, move around on their own, and must be carried by ocean currents. Next are the chiton, very ancient animals that live on the ocean floor. Their body is made up of 8 chitinous plates that protect their soft underside. They use many crude legs on their underside to move along the ocean floor, finding food. Next on the evolutionary chain in the phylum are the snails and slugs. Snails use the calcium carbonate in their mantle to form a hard, protective shell around their visceral mass. Both snails and slugs use the musclular foot on their ventrical surface to slowly move along the ground. The phylum ends with the squid and the octopus. These animals are some of the most advanced invertibrates, with eyes resembling those of the vertibrates. They also have a much more advanced nervous system, with an actual brain capable of learning things. However, the shell is greatly reduced in the squid, seen only in the thin plastic-like quill along the top of their visceral mass. So, the molluscs are more advanced as even the most basic of them have strong chitinous shells for self defence. The respiratory and circulatory systems are much more efficient. The more motile species are capable of more coordinated and speedy movement. And, almost vertebrate-like qualities can be observed in the cephalopods, such as the advanced eyes, and the advanced nervous system capable of basic behaviors and memorization.

The tough exoskeletion of the following phylum sets these animals appart. This is the phylum Arthropoda; the insects, arachnids, and the crustaceans. While evolution is not as apparent throughout the classes in this phylum, the insects are by far the most dominant animals in the phylum. This phylum makes up 75% of all animals on earth. The major advancement of this phylum is the appearence of a skeleton. The exoskeleton is located on the outside of the body, and forms a strong plating around the vulnerable innards of the animal. This exoskeleton is broken up by joints, which allow for movement. With the exoskeleton comes the formation of jointed walking legs, which allow for very fast and coordinated movement, especially on land. The exoskeleton provides immense strength-to-body ratio, allowing for these animals to do tasks that would normally impossible. The exoskeleton also provides excellent protection for the arthropods. The closed circulatory system returns in the arthropods, but instead of having veins and arteries, the blood is spread out through the body in blood cavities. Their digestive system is identical to previous phylums. The respiratory has also advanced, with insects posessing spicules under their hind legs on their abdomen, spiders have book lungs, and crustaceans have more advanced gills. This means that, excluding the crustaceans, the animals do not have to stay moist to respirate. Specialized segmentation also changes, with arachnids and crustaceans having an abdomen and cephalothorax, and the insects having a head, thorax, and abdomen. Insects have wings, which enables them to be the only invertebrates capable of flight. Decreased size of the animals, combined with their camoflauge patterns, enables them to easily hide and avoid predators. They reproduce at an extremely rapid rate, so it is very easy to maintain and grow their species population. So, the development of more efficient respiratory systems, a stong exoskeleton, and the ability to fly, among many other advances in defence and hunting.

At this point, it almost appears as if evolution has taken a step back with the phylum Echinodermata; the sea stars. The animals in this phylum lose the segmented body plan that has been developed in the previous phyla. They lose the enhanced circulatory and respiratory systems as well. However, the major development in this phylum is the watervascular system. This system is exclusive to this phylum, and covers the needs of the circulatory and respiratory system. Water enters through the madreporite and is spread throughout the body to carry oxygen to the muscles. This system essentially replaces the blood of previous phyla with water. This phylum also has a unique digestive system; to feed, it inverts its cariac stomach out of its mouth into an open bivalve, melts down the insides, then absorbs it into its pyloric stomach, where nutrients are absorbed throughout the body by the watervascular system. This is the only phylum that has pentaradial body symmetry. The sea stars also redeveloped the ability to reproduce by fragmentation, as well as to regrow lost limbs. They also show the first development of an internal skeleton, with flecible calcarious plates embedded in the flesh of the sea star. So, the development of the watervascular system, the ability to regrow limbs, and the basic endoskeleton are the advances in the phylum Echinodermata over the other phyla.

Finally, we have reached the chordates. The evolution of the classes and orders within this phylum are far greater than any other phylum. The phylum begins with the most basic of the chordates; the lower chordates. Excluding the subphyla Hemichordata, these are the first animals to develop a notochord with a dorsal nerve cord. The notochord is a basic spinal column made of cartilage that runs up the dorsal side of the animal, beside the nerve cord. However, the notochord is only present in some forms of some of the lower chordates. For instance, while the notochord can be found in the larva of subphyla urochordata, it disappears, along with the nerve chord, when the larva grows into adult form. The final subphylum of the lower chordates, the Cephalochordates, display the four general characteristics of chordates, and are thus named the classic chordate. These characteristics are, 1. Posessing a notochord, 2. Posess a dorsal hollow nerve chord, 3. Posess pharyngeal gill slits, and 4. Posess a muscular, post-anal tail. Almost no animals posess all of these traits during their adulthood, or at one time, but they posess them all at some point in their lives. These animals show the transition between the vertibrates and invertibrates. So, the Lower chordates are more advanced as they have a notochord, a nerve cord, gill slits, and a tail at some point in their lives, the most crutial of these being the notochord and nerve cord, which will eventually lead to the complex nervous structure seen in humans.

The next subphylum are the vertibrates. This phylum begins with the fish. The fish are the first animals to display a complete endoskeleton, with a real vertebral column surrounding the nerve cord. The fish also posesses a nodochord, but this is mostly in the larva, and is reduced or absent in the adults of these larvae. The fish have a closed circulatory system with a more developed heart comprised of one atrium and one ventricle. This makes the spread of oxygen and nutrients throughout the body very efficient. The class Osteichthys have a very advanced nervous system and brain. It is in this class that we see the first development of behaviors, including schooling, and spawning patterns. Reproduction occurs with males releasing sperm and females releasing eggs. Young are required to be able to swim when born. Some fish can travel over land for short distances. Fish belonging to the phylum Chondrichthyes, the sharks, have a skeleton amde entirely of cartilage not bone. They have an extremely streamlined body allowing for much faster movement than other aquatic animals. They have a very well developed sense of smell used for hunting. And, unlike the other fish sharks offspring are fertilized and developed internally. So, the advances of this phylum are the development of the spinal column containing the nerve cord as well as a more efficient circulatory, respiratory and nervous system.

As evolution continued, aquatic animals such the fish began to develop appendanges. The first aquatic animals to move on land belong to the class Amphibia; the frogs and salamanders. Frogs began their lives as larvae just like the fish. This larvae called tadpoles lived exclusively in the water. These tadpoles undergo metamorphasis to become air-breathing, land dwelling adults with legs. They have a newly developed respiratory system consisting of crude sac like lungs branching off the pharynx. These lungs were very inefficient; fifty percent of oxygen was still absorbed throught the skin meaning they had to stay moist. They also had a heart with three chambers, the new chamber being a second atrium holding oxygenated blood. Blood mixes in the ventricle to form partially oxygenated blood. This system was very inefficient. Their skeletal plan meant their legs were off to the side resulting in cumbersome movement over land. The one majorly improved system was the nrevous system. The brain size grew considerably resulting in improved senses. So, the advances of the phylum Amphibia are its ability to live on land and in water, its newly developed but less efficient circulatory and respiratory systems and its advanced nervous system.

Animals continued to evolve and live permanently on land.The next class' members are very well adapted to life on land and in the ocean. This is the class Reptilia; the snakes, turtles, lizards, crocidiles and tuatara. The major evolution of this class is the amniotic egg. This egg removed the problem of embryos having to remain in the water by keeping the water and the embryo inside the mother. This also meant that internal fertilization was not required. The respiratory system was greater improved over that of the amphibians. More advanced lungs meant that they no longer neede to bring oxygen in through their skin. this meant they didn't need to stay moist, and they could cover theiry skin with scales or shells. The circulartory system was still fairly inefficient as mixing still occurred in the ventricle. The brain continues to grow resulting in better sensory organs as well as specific behaviours like territoriality. Legs now grow out of the bottom of the body allowing for faster movement. Animals in the order Chelonia developed hard shells covering their internal organs which they can hide in for self defense. Members of the order Crocidilia are the only reptile with a four chambered heart resulting in an efficient circulatory system. Animals in the order Squamata are able to live in arid climates by excreting uric acid (precursor to urine) to conserve water. In snakes specifically they defend themselves by injecting venom into their targets by biting them with sharp fangs. So, the introduction of the amniotic egg, the improvements of the circulatory and respiratory systems, ability to live in dry climates, and increase brain capabilities are the advancements of this phylum.

The next class lives exclusively on land - or over it. This is the class Aves; the birds. These animals are the only vertebrates truly capable of flight. They have the ability to maintain a constant body temperature, regardless of the environment. The amniotic egg is present, but the bird has to incubate it. The egg has a calcified shell so it can survive outside the body. These are first offspring that require post natal care. The continuing development of the brain results in a excellent sense of sight. All members of the class have a four chambered heart, providing the maximum amount of oxygen for the heart. They have air sacs attached to the wings in addition to much more efficient lungs for respiration. So, the class Aves are more evolved mainly because they can fly but also due to their post natal care, development of the brain, and a more efficient circulatory and respiratory systems.

The final class is the most advanced of all the animals on the planet. This very diverse class is class Mammalia; the mammals. They have a complete circulatory system with a four chambered heart and full circulatory pattern. They have highly efficient respiratory systems. Their efficient lungs are aided by the muscular diaphragm below the lungs. The diaphragm changes the pressure by expanding and contracting to control the flow of air in the body. The majority of the body is covered in hair for insulation and sensing, which are modified scales. They have a large layer of subcutaneous fat for insulation and food storage. The offspring grow internally with an amniotic egg modified to include a placenta. The young require extensive post natal care and are nursed by mammory glands. They have the most advanced nervous system with a great increase in brain size. Behaviour abilities reached learning and reasonong levels as well as forming societies. Limbs are well adapted for movement accross the land. Many mammals also have adaptations of limbs for water and short air travel. So, the advancements of the class Mammalia are the amniotic egg with a placenta, and a large positive change in all the body systems.

In my opinion the most adapted organism to life on Earth are the Cnidarians; the jellyfish. These animals, while very basic compared to the other phyla, have many characteristics that no other animal has. Jellyfish are nearly impossible to kill as they have very dangerous defensive body parts (cnidocytes) and can reproduce by fragmentation. If people do attempt to kill them they release all their egg and sperm at once in fear. This results in the mass fertilization and development of new jellyfish. Jellyfish are ninety-five percent water which means they have little to no predators as they are not edible and have essentially no nutrients in their body. This also means that humans do not fish for them which has been one of the leading causes of species depletion in the oceans today. Jellyfish also have the incredible ability to survive in areas of ocean where no oxygen is present for extended periods of time. Finally jellyfish have basic mating instincts where they gather into very large swarms to release their eggs and sperm. This results in many new jellyfish polyps. The polyps are also beneficial as they can reproduce by budding constantly for an indefinite amount of time. So, the Cnidarians are the most advanced due to their self-defense, reproductive methods, their ability to avoid being hunted and their ability to survive in environments where other living beings cannot.

In my opinion my portfolio is an excellant piece of evidence supporting the theory of evolution. Even just looking at the pictures throughout all the labs clearly shows the advances of both external and internal features of the body. My conclusion also provides a clear and concise timeline of evolution including changes in behaviour senses and all the body systems. It is hard to deny the sound evidence of the pictures which is why my portfolio is a solid piece of evidence for the theory of evolution.